The Lower Palaeozoic apparent polar wander path for Baltica: palaeomagnetic data from Silurian limestones of Gotland, Sweden

Abstract

SUMMARY Well-dated and undeformed Silurian (Lower Wenlock) limestones from Gotland, southern Sweden, yield two stable remanence components following detailed thermal and alternating-field demagnetization studies. (1) A low blocking-temperature/coercivity magnetization, termed L, delineated below 250dC/10mT, is oriented parallel to the present Earth's field (Dec. 001, Inc. +67, n= 4 sites, a95= 16d). (2) A higher blocking-temperature/coercivity magnetization, termed H, unblocked between 250-400dC/10-35mT, has a NNE declination and shallow negative inclination (Dec. 025, Inc. -19, n= 5 sites, a95= 5d). This H component direction compares favourably with a previous result from Gotland based upon blanket cleaning. Given a lack of evidence for subsequent geological heating (Conodont Alteration Index = 1-1.5), or pervasive palaeomagnetic overprinting, the H palaeopole is regarded as reliable and primary/early diagenetic in origin (19dS, 352dE, dp/dm 3/5). The only other well-constrained Mid-Silurian pole from Baltica, that from the Ringerike Sandstone of the Oslo district, is in excellent agreement with the Gotland data. These combined poles resolve previous problems regarding the shape and time-calibration of Silurian apparent polar wander relative to Baltica.